The present invention relates to storage-stable, one-component polyurethane compositions which cure at elevated temperature and to the use of these compositions in coatings and sealants.
Polyurethane compositions which cure to form coatings and sealants are well known. The known compositions include both one-component and two-component systems. From a practical standpoint, one-component systems are preferred because they are much easier to handle and to use. They do, however, require storage in the absence of moisture if they will not be used shortly after they are produced.
U.S. Pat. No. 3,865,791 discloses one-component systems composed of a polyisocyanate and at least one compound selected from polyenamines, enamines having aldimine or ketimine groups, enamines having a hydroxy group, and prepolymers formed by reacting a polyisocyanate with a hydroxy-enamine. Prepolymers formed by reacting the disclosed enamines with a polyisocyanate may be combined with a second isocyanate which second isocyanate may be capped. This composition is cured by the addition of water or by exposure to atmospheric moisture.
U.S. Pat. No. 3,886,228 discloses single package curable polyurethane compositions containing a polyisocyanate which may be blocked and a curing agent. The curing agent is a condensation product obtained by reacting approximately equimolecular proportions of diethylene triamine or triethylene tetramine with an anhydride selected from phthalic anhydride, hexahydrophthalic anhydride, maleic anhydride and succinic anhydride. These disclosed compositions are sensitive to water, alcohols and other compounds containing active hydrogen atoms. Partial blocking of the isocyanate groups of aromatic isocyanates with phenols, alkyl phenols, polyphenols or phenolic novolacs are taught to reduce sensitivity of the disclosed compositions to active hydrogen atoms without significantly decreasing the shelf-life or curing rate at elevated temperature. The compositions described in this disclosure cure over an extended period of time (even at elevated temperatures) and have a Durometer hardness of less than about 50 Shore D.
U.S. Pat. No. 3,743,626 discloses hydrocurable oxazolidine-isocyanate compositions which cure in the presence of moisture without substantial heating.
U.S. Pat. No. 4,118,376 also discloses hydrocurable compositions made up of an oxazolidine compound and a prepolymer containing free isocyanate groups. These prepolymers are formed by reaction of a polyisocyanate with dispersions which have been synthesized in situ in a dispersing media of polyhydroxyl compound. The polyhydroxyl compound is substantially more reactive with isocyanates than the dispersing media. The preferred dispersions are dispersions of isocyanate-hydrazine or hydrazine hydrate in a polyhydroxy polyether.
U.S. Pat. No. 4,595,445 discloses adhesive compositions which set at elevated temperatures. These compositions are made up of a finely-divided polyisocyanate of retarded activity of which 0.1-25% of the isocyanate groups are surface modified, a polyamine and optionally, a polyol.
U.S. Pat. No. 4,619,985 discloses deactivated suspensions of finely divided polyisocyanates in deactivated, relatively high molecular weight polyols and/or polyamines. The polyols and/or amines are deactivated by addition of substances which have an acylating, neutralizing, alkylating or adsorbing effect.
U.S. Pat. No. 4,624,996 discloses a heat curable one-package polyurethane resin composition which is made of an isocyanate-terminated prepolymer having isocyanate groups blocked by an oxime and a curing agent having at least two active hydrogen atoms per molecule. Polyamines blocked by reaction with an anhydride are among the curing agents disclosed.
U.S. Pat. No. 5,124,447 discloses one-component polyurethane or polyurea compositions which cure at ambient temperature. These compositions are made up of a) a liquid polyisocyanate having isocyanate groups blocked with a phenolic blocking agent and b) a solid polyamine salt which is insoluble in and dispersed throughout the liquid blocked polyisocyanate. The polyamine salt is the reaction product of a polyamine with an organic or inorganic acid.
U.S. Pat. No. 5,142,014 discloses a one-component polyurethane or polyurea composition which cures at ambient temperature which is made up of a) a liquid polyisocyanate in which the isocyanate groups are blocked with a phenolic blocking agent and b) a solid polyamine internal salt which is insoluble in and dispersed throughout the blocked liquid polyisocyanate a). The solid internal polyamine salt contains at least two primary or secondary amino groups and at least one organic acid group. Among the solid polyamine internal salts described as preferred is the reaction product of phthalic acid anhydride and diethylene triamine.
U.S. Pat. No. 5,138,011 discloses one-component polyurethane or polyurea compositions which are made up of a) a liquid polyisocyanate in which the isocyanate groups are blocked with a phenolic blocking agent and b) a solid polyamine which is insoluble in and dispersed throughout the liquid blocked polyisocyanate a). The solid polyamine must remain stable in the presence of the polyisocyanate component for at least one week when stored at ambient temperature. Among the polyamines described as being useful in these compositions are the trans/trans isomer of 4,4'-diaminodicyclohexyl methane, 4,4'-diamino diphenyl methane and 2,4-diamino-toluene.
U.S. Pat. No. 5,264,515 discloses moisture curable compositions in which a moisture curable base and a curing agent which does not contain molecular water but which produces water upon activation to cure the curable base. The shelf life of the curable composition may be extended by coating either the particulate curing agent or one or more of the components of the composition with a material that is meltable or frangible.
Many of the known one-component systems have the disadvantage of requiring the addition of a curing agent, such as water, or exposure of a substrate to which the composition has been applied to a curing agent such as atmospheric moisture. The addition of a curing agent to the composition shortly before it is applied to a substrate, requires thorough mixing of the curing agent to get even cure and limits the amount of time in which the curing composition must be applied to a substrate. Exposure of the composition to a curing agent after it has been applied does not have these disadvantages. However, the exposure curing method is disadvantageous because the cure obtained when the composition is applied at higher thicknesses is uneven. The outermost portion cures more quickly than that portion which is not directly exposed to the curing agent.
U.S. Pat. No. 4,469,857 discloses a two-component system for the production of a synthetic resin compound capable of curing in the absence of moisture which system is made up of a first component which includes a polyisocyanate and an enamine and a second component which includes a carrier compound having water aggregated thereto.
A one-component polyurethane or polyurea composition which cures evenly without the need to add a curing agent or to expose a coated substrate to a curing agent would be advantageous.